Polyesters that are crystalline and have high heat distortion temperatures along with other good molding and film properties are becoming more and more in demand in such applications as fibers, photographic film, computer boards and other applications that require a polymer to be crystalline, orientable, subject to heat-set and which can withstand high temperatures. A copolyester system which is crystalline, suitable for high temperature end use and has practical application in film, fibers and molded parts, and packaging has now been unexpectedly found.
Two patents, U.S. Pat. Nos. 2,901,466 and 3,161,710, and Research Disclosure 29481 (October, 1988) mention copolyesters comprised of dimethylterephthalate, dimethyl 2,6-napthalene dicarboxylate and 1,4-cyclohexane dimethanol. These patents and disclosure are concerned with polymers and copolymers of poly (1,4-cyclohexylene dimethylene terephthalate) and copolymers thereof. They mention copolymers containing up to 50 mole percent 2,6-napthalene dicarboxylic acid, and there is no mention of isomer ratios in copolyesters of poly (1,4-cyclohexylene dimethylene terephthalate) with dimethyl 2,6-napthalene dicarboxylate. Copolyesters containing from 1 to 99 mole percent 2,6-napthalene dicarboxylate or 1 to 99 mole percent of terephthalate and 0 to 100 mole percent cis isomer of 1,4-cyclohexanedimethanol and all copolyesters containing all cis/trans isomer ratios between 0 and 100 percent are presently of particular interest.